A combination of in situ high-pressure neutron diffraction at pressures up to 17.5(5) GPa and molecular dynamics simulations employing a many-body interatomic potential model is used investigate the structure cold-compressed silica glass. The give good account results existing x-ray ~60 GPa. On basis results, an atomistic for densification proposed which rings are "zipped" by pairing five- and/or sixfold coordinated Si sites. gives accurate description dependence mean primitive ring size ⟨n⟩...

A classical application of the Car-Parrinello method in computer simulation ionic systems is demonstrated. The induction effects interionic interactions are included addition to short-range repulsion and dispersion described by effective pair potentials. By representing induced dipoles as a dynamically variable charges fixed on ends rod extending Lagrangian accordingly, self-consistent at each time step generated from values previous step, without need for explicit minimization....

A computer simulation of amorphous ${\mathrm{SiO}}_{2}$, with a potential which includes formal ionic charges and an explicit account polarization effects, produces calculated infrared spectrum in good agreement experiment. The effects play crucial role reproducing the observed network vibrational frequencies allowing for correct distribution intensity across spectrum.

Phase transitions in the liquid state can be related to pressure-driven fluctuations developed density (i.e., inverse of molar volume; ρ = 1/V) or entropy (S(T)) rather than by gradients chemical potential (μ(X), where X is composition). Experiments and simulation studies now show that such are likely exist within systems with a wide range bonding types. The observations permit us complete trilogy expected responses changes P T as well μ(X), case among crystalline solids. Large...

The origin of the first-sharp diffraction peak (FSDP) in supercooled liquid ${\mathrm{ZnCl}}_{2}$ (a network-forming, intermediate strength fluid) is studied by computer simulation. Measures are introduced to characterize voids spatial distribution cations and existence transient layered structures clarify their role producing FSDP. It shown that position FSDP set mean intervoid separation its intensity due density fluctuations with a character even well above glass transition.

Computer simulations with polarizable anions are shown to reproduce the distinctive prepeak observed in diffraction studies of molton ${\mathrm{ZnCl}}_{2}$ and its mixtures alkali chlorides. Two distinct origins for peak microscopic structure melts identified. The influence cation size on behavior is explained. relationship between observation prepeaks existence network structures strong ionic liquids discussed.

Using a previously derived model of the dry, amorphous, hydrophilic SiO2 surface, reactivity generic defect sites on surface with respect to water, and local network rearrangement that accompanies hydrolysis at these sites, is investigated using cluster models. Ab initio methods are used calculate reaction barriers pathways. Consequences various types product found discussed reference potential for polymer chemisorption hydrolyzed, amorphous surface.

A low- to high-density pressure-driven phase transition in amorphous silicon is investigated by synchrotron x-ray diffraction the diamond anvil cell. Complementary atomistic molecular dynamics computer simulations provide insight into underlying structural transformations and allow us interpret structure factors obtained from experiment. During compression form of scattering function $S(Q)$ changes abruptly at $13.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, indicating significant...

The diffusion of sodium and carbonate ions in molten is investigated by quasi-elastic neutron scattering (QENS) at T = 1143 K. small wave vectors dominated diffusing ions, the derived self-diffusion coefficient DNa 4.5 × 10–5 cm2/s agrees well with previous tracer measurements. from anion coherent, coherent dominates QENS signal a modulus greater than 1 Å–1. line width function used to obtain this temperature DCO32– 2.4 cm2/s, again agreement values studies. results measurement are larger...

The structural effect of inserting large central rings into a two-dimensional network three-coordinate nodes is investigated using ring-growth Monte Carlo procedure. size the ring systematically varied, as inherent level disorder in surrounding (as controlled by “temperature” and characterized fraction six-membered rings). on overall topology analyzed terms both topological geometric distances. For larger rings, first shell becomes exclusively populated four- five-membered which leads to an...

A representation of the short-range repulsion energy in an ionic system is described which allows for fact that ion may be compressed by its neighbours. The total expressed a pairwise additive form, but interionic interactions have many-body character. form this and parameters required to represent MgO CaO are obtained from recent ab-initio electronic structure calculations. transferable between crystals with different coordination number demonstrated direct comparison results on crystal...

The partial radial distribution functions galpha beta (r) and structure factors Salpha (k) obtained in computer simulations of the ionic melts stoichiometry MCl2 with a recently introduced polarizable ion model are described. calculated quantities exhibit distinctive structural features which have been discovered experimentally attributed to 'covalency'. These include shift position principal peak g++(r) relative g--(r) decreasing cation size pre-peak S++(k).

Network-forming liquids comprising tetrahedral motifs are investigated by large-scale molecular dynamics computer simulations within the framework of an ionic interaction model. The network topology is controlled varying anion polarizability, which governs intertetrahedral bond angle, for different system densities. A coupling found between growth in magnitude and range extended oscillations appearance ordering on intermediate length scale. interrelation fragility structural arrangements...

Amorphous graphene is a realization of two-dimensional Zachariasen glass as first proposed 80 years ago. Planar continuous random networks this archetypal network are generated by two complementary simulation methods. In the first, Monte Carlo bond switching algorithm employed to systematically amorphize crystalline sheet. second, molecular dynamics simulations utilized quench from high temperature liquid state. The approaches lead similar results detailed here, through pair distribution...

Computer simulations of a range molten salts stoichiometry MX3 using polarizable, formal charge ionic interaction model are described. The systems studied — LaCl3, TbCl3, and YCl3 span cation sizes the is “generic” one, in sense that size only parameter potential which distinguishes one system from another. liquid structures predicted compared with recently obtained neutron diffraction data. Excellent agreement found, except first coordination shell seems to be too tightly bound computer...

The predictions of an “extended” ionic interaction model for the phonons and other properties crystalline MgO are considered. In extended model, polarization interactions resulting from dipoles quadrupoles induced on oxide ions by both Coulombic short-range with explicitly represented. Furthermore, shapes ions, as perceived through repulsive their immediate neighbors, allowed to respond instantaneous coordination environment. Shape deformations spherical (breathing), dipolar quadrupolar...

Abstract Computer simulations of a range ionic systems stoichiometry MX3 using polarizable, formal charge interaction model are described. The objective the present work is to describe optimization potentials in light new structural information which has become available from neutron scattering studies liquid. As well as substantially improving agreement with experiment for LaC13, TbC13, YC13 and A1C13, simulation results presented first time ScC13, shown exhibit fascinating crosslinked...

Many binary systems (and their mixtures) which might be expected to `ionic', from electronegativity considerations, are found exhibit pronounced `covalent effects' in condensed-phase structure and dynamical properties. Recent work, involving both electronic calculations computer simulation, has suggested that the interactions arise describable within ionic model - provided many-body effects, whose origin is change an ion's properties caused by interaction with its environment, included. In...